Classical teaching, supported by the big organizations (NSCA, ACSM), is that 60-85% of 1RM is optimal for muscle hypertrophy. This is however, being challenged by recent experimental evidence. For example, one study showed that 30% vs 90% of 1RM were similar. Subsequently, this has become an area of debate among researchers and weightlifters over optimizing muscle hypertrophy.

The dogma for muscle strength is a little more well established, meaning high load is superior to low load resistance training. For example, 80% of 1RM is superior to 30% of 1RM for strength gains.

What is not well understood is how high-load and low-load influence neuromuscular adaptations. Examples of neuromuscular adaptation from resistance training include neural pathways linked to target muscles become more efficient at transmitting the message; the timing of contractions becomes more coordinated and it can reduce neuromuscular fatigue.

They took 15 untrained men (21 years, weight 84 kg or 184 lb), randomly assigned to either a high-load (n = 7) or low-load (n = 8) resistance training group and completed forearm flexion resistance training to failure 3 times per week for 4 weeks.

Researchers Measured (baseline, week 2, week 4)

Forearm flexor muscle thickness (MT)

Echo intensity

Maximal voluntary isometric contraction (MVIC)

1RM strength,

The electromyographic,

Mechanomyographic (MMG),

Percent voluntary activation (%VA) responses at 10–100% of MVIC

Results

The muscle thickness increase (aka hypertrophy) was similar between both groups.

As for neuromuscular adaptations, there were no significant differences between the groups.

The mechanomyography (MMG) amplitude at 80 and 90% MVIC decreased from baseline to week 4, and percent voluntary action (%VA) increased at 20 and 30% MVIC for both groups and these changes were independent of the training loads.

Conclusions

Muscle hypertrophy was equivalent at the end of 4 weeks of resistance training when using either 30% or 80% of 1RM.

Muscle strength development was superior when training at 80% of 1RM

These strength adaptations were not explained by neuromuscular adaptations because changes were subtle and similar in both groups.

Ultimately, more research is needed to understand high- vs low-load on neuromuscular adaptations